Five Reasons Why Do Parkinson’s Patients Lose Their Sense of Smell?

Why do Parkinson's patients lose their sense of smell?

Loss of smell, or anosmia, is a common but often overlooked symptom of Parkinson’s disease. Many patients experience this sensory change even before the more well-known motor symptoms like tremors and stiffness appear. Understanding why this happens can provide valuable insights into the early detection and management of Parkinson’s disease.

Here are five key reasons explaining why Parkinson’s patients may lose their sense of smell.

1. Neurodegenerative changes

Parkinson’s disease is primarily a neurodegenerative disorder, which means it causes the gradual degeneration of nerve cells in the brain. One of the earliest areas to be affected is the olfactory bulb. This part of the brain is responsible for our sense of smell. As Parkinson’s disease progresses, the olfactory bulb loses its ability to process and interpret odors effectively. This leads to a diminished or complete loss of smell. This problem begins subtly and often goes unnoticed by the affected individuals until it becomes more pronounced.

The loss of smell due to neurodegenerative changes in the olfactory bulb can significantly impact the quality of life. It affects the ability to enjoy food and detect potentially dangerous odors like smoke or gas. Early detection of changes in the sense of smell can therefore be a critical early indicator for diagnosing Parkinson’s disease.

2. Dopamine deficiency

Dopamine is a neurotransmitter that plays a crucial role in transmitting signals within the brain. This brain chemical is significantly impacted in Parkinson’s disease. While dopamine is primarily known for its role in regulating movement and coordination, it also influences other sensory experiences, including smell.

The reduction in dopamine production associated with Parkinson’s can disrupt the normal functioning of olfactory pathways. As such, it impairs the sense of smell. This disruption is not only due to the lower levels of dopamine itself but also because dopamine deficiency affects the brain’s ability to integrate sensory information. As a result, patients might find that their ability to detect and differentiate smells becomes increasingly impaired.

3. Presence of alpha-synuclein proteins

Research has shown that abnormal alpha-synuclein proteins are found in the olfactory bulb in the early stages of the disease. These proteins can form clumps, known as Lewy bodies, and interfere with the normal functioning of neurons. This disruption can lead to the loss of smell as these proteins accumulate and affect the neurons responsible for detecting and interpreting odors.

The accumulation of alpha-synuclein in the olfactory bulb not only impairs the sense of smell but also suggests that olfactory testing could be used as an early diagnostic tool for Parkinson’s disease. Furthermore, understanding how alpha-synuclein impacts olfactory neurons may offer insights into the progression of Parkinson’s disease. This can guide the development of targeted therapies aimed at preventing or slowing the aggregation of these proteins.

4. Reduced regeneration of olfactory neurons

In a healthy brain, olfactory neurons have the ability to regenerate, which helps maintain a functional sense of smell throughout life. However, in Parkinson’s patients, this regeneration process is impaired. The exact reason for this impairment is not fully understood. It is believed to be linked to the overall decrease in brain cell regeneration associated with the disease. This diminished regenerative capacity means that once olfactory neurons are damaged, they are less likely to recover, leading to a progressive loss of smell.

The impairment of neuronal regeneration in Parkinson’s disease could be due to a combination of factors. It could be due to oxidative stress, mitochondrial dysfunction, and the toxic effects of accumulated proteins like alpha-synuclein. Researchers think that understanding and potentially reversing this impairment could open new opportunities for treatment, not only for the restoration of smell but also for broader neuroprotective strategies in Parkinson’s disease.

5. Inflammation in the olfactory system

Chronic inflammation is another aspect of Parkinson’s disease that can contribute to the loss of smell. Inflammation in the olfactory system can damage sensory receptors and neural pathways, further impairing the sense of smell. Ongoing research continues to explore how inflammation affects Parkinson’s symptoms, including olfactory dysfunction.


The loss of smell in Parkinson’s patients is influenced by a combination of neurodegenerative changes, dopamine deficiency, accumulation of alpha-synuclein proteins, reduced regeneration of olfactory neurons, and inflammation. Understanding these factors not only helps in managing the symptoms more effectively but also aids in the early diagnosis of Parkinson’s disease.

If you or someone you know is experiencing a significant change in the sense of smell, it is advisable to consult a healthcare provider for further evaluation and to discuss potential links to neurological conditions like Parkinson’s.

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